How do you water your houseplants? Every day? Each Tuesday? Fill a coffee cup and give it to your plants every once in a while? Houseplants are probably killed or injured more often by improper watering than by any other single factor. No general schedule can be used for watering all houseplants. Size of plant, pot, light, temperature, humidity and other conditions influence the speed with which the soil mass dries out.
When to water
In general, flowering plants need more water than foliage plants of the same size. Never water any plant unless it needs it. Soil kept either too wet or too dry causes plant roots to die, which leads to poor growth or death of the plant. Never allow plants to wilt, and never allow them to stand in water for long periods of time.
Learn to gauge the moisture content of the soil by its color and feel. As the soil surface dries, it becomes lighter. Under continued drying, the soil begins to crack and pull away from the sides of the pot. When severe drying occurs, some damage already will have been done to the roots. Soil kept too moist becomes sticky and slimy, thus inviting root rots and other disease problems.
Kinds of water
Ordinary tap or well water is usually satisfactory for plants. Chlorine and fluorine often added to city water do not harm plants. Rainwater and melted snow are excellent water sources. Water run through most water softeners, however, should not be used continuously for watering potted plants.
How to water
Plants may be watered from either the top or the bottom of the pot. If you prefer watering from the top, use a watering can with a small spout and keep as much water off the foliage as possible. Each time, wet the entire soil mass, not just the top inch. Add water until it comes through the drainage hole in the bottom of the pot. Discard water that remains beneath the pot one hour after watering.
Watering from the bottom ensures thorough wetting of the soil mass. Place the pot in a pan or saucer filled with water, or dunk the pot to just below its rim in a deep bucket of water. When the top of the soil becomes moist, the entire soil ball should be wet. Remove the pot, allow it to drain, and return it to the saucer.
Salts may form a white accumulation on the soil surface if plants are watered regularly from the bottom. Occasional watering from the top helps wash out the salts. Don’t allow the soil to reabsorb any water that has been run through the soil to leach out salts. If surface salt accumulation becomes too heavy to remove in this way, scrape off the surface soil and replace it with fresh soil. Try not to injure plant roots.
Drainage
Potted plants should always have good drainage. Occasionally, the drainage hole may become clogged by roots. Check it by pushing a finger, stick or pencil into it. Even if drainage from the pot is good, pot coverings can hold water. Pots wrapped in waterproof foil or placed in deep planters should be checked occasionally for standing water.
Plants with “wet feet” soon look sick — leaves yellow or drop, flowers collapse, and normally healthy white roots turn brown. Any or all of these symptoms can result from stagnation of the water, too little soil oxygen and development of diseases that rot the roots.